Ribbon cartridges for typewriters provide convenient, more clean-handling loading and unloading. The cartridge originally contains the supply spool of transfer medium, mounted to be controllably unwound, and a hub mounted to wind up the used ribbon.
Free unwinding of the take-up spool when the cartridge is off the typewriter can result in tangling of the ribbon. Also, insertion of a cartridge when the ribbon may unwind requires the operator to tighten the ribbon manually and to assure that used ribbon has been wound past the printing position. Where the cartridge design includes a high-friction contact with the take-up spool, such as, for example by the internal leaf spring in U.S. Pat. No. 3,356,202 to W. Goff, Jr., back checking by the friction is inherent and a special mechanism is unnecessary. In other designs the size of the ribbon or other physical relationships render unwinding an insignficant problem.
A known prior cartridge such as described in the published article by E. J. Lenney entitled "Ribbon Drag Wire" in the IBM Technical Disclosure Bulletin, Vol. 18, No. 4, (September 1975), at p. 1093, employs a wire wrapped around the hub of the supply spool in a cartridge as a friction brake. One end of the wire is anchored in the cartridge and the ribbon rides upon a depending leg at the other end. As the ribbon is fed, it pulls on the end it rides upon to open the portion wrapped around the hub. This frees the supply spool to move. In accordance with this invention, an internal wire mounted in a ribbon cartridge has an end contacting the hub of the take-up spool. The end is positioned to engage the hub when it moves counter to the take-up direction and to slide freely with the hub when it moves in the take-up direction. This provides physical resistance to unwinding at any angular position.
Braking assemblies for machinery having similar one-direction engagement are found in U.S. Pat. No. 81,729 to Baker and U.S. Pat. No. 131,402 to Kingry et al. U.S. Pat. No. 3,409,113 to McLean discloses a spring biased, centrally pivoted, inflexible brake member having an eccentric face as a braking surface which operates against a frame-mounted take-up spool in a typewriter. No prior art is known similarly employing the end of a flexible member to prevent unwinding in a cartridge.
Accordingly, in accordance with this invention a single wire member positioned in contact with the hub provides an economical structure which acts to prevent unwinding of the hub at any position the hub adopts. Typical alternatives to provide positive holding, as distinguished from frictional holding, would involve pawls, ratchets and the like, mounted in the cartridge or off the cartridge in a ribbon-feed mechanism, which would be more intricate and expensive and yet not infinitely variable in position of operation.